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Two new North American butterflies
Vol 20, Iss 1, Page 5
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The vegetation of the Fort Reliance sand-plain
Vol 20, Iss 1, Page 9
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Notes on some American butterflies mainly relating to classification and nomen-clature. Parts 2 and 3
Vol 20, Iss 1, Page 39
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Crawfishes of the Southern Appalachians and the Cumberland Plateau
Vol 20, Iss 2, Page 61
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List of types of Crustacea in the Carnegie Museum on January 1, 1931
Vol 20, Iss 2, Page 161
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List of types of Pelecypoda in the collections of the Carnegie Museum
Vol 20, Iss 2, Page 171
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List of types of Amphineura and Gastropoda in the collection of the Carnegie Museum on January 1., 1931
Vol 20, Iss 2, Page 179
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Notes on some American butterflies, mainly relating to classification and nomenclature. Pt. 3 (Cont’d from p. 55).
Vol 20, Iss 2, Page 255
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An undescribed water strider from Brazil (Hemiptera-Gerridae)
Vol 20, Iss 2, Page 267
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Leptoypha, an American genus hitherto unknown as occurring in Palearctic Asia. (Hemiptera, Tingitidae)
Vol 20, Iss 2, Page 269
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A new subspecies of the Arizona Gray Squirrel (Sciurus arizonensis Coues)
Vol 20, Iss 2, Page 271
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Earl Douglass. A sketch in appreciation of his life and work
Vol 20, Iss 3-4, Page 279
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The Upper Uinta Formation of northeastern Utah
Vol 20, Iss 3-4, Page 293
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New species of the genus Teleodus from the Upper Uinta of northeastern Utah
Vol 20, Iss 3-4, Page 307
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A list of the land-snails of Pennsylvania, with a summary of their distribution
Vol 20, Iss 3-4, Page 313
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New Mesonychids from the Uinta
Vol 20, Iss 3-4, Page 333
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Two new species of Agriochoerids
Vol 20, Iss 3-4, Page 341
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Errata and Corrigenda
Vol 20, Page ix